DaveP

Hmmm… not sure that the T5403 is well suited for high-altitude balloon work; the datasheet indicates that the low end of its sensitivity is at 300hPa, or approx. 9.1km / 30,000 ft. For reference, StillDavid’s flight that reached 130,000 feet would have seen something like 3.5hPa.

There are a couple of groups discussing doing just that on diydrones.com, and there’s also a commercial solution to do that from GPS Boomerang. I would caution, though, that the regulations are unclear at best for attempting such a flight in the US National Airspace.

Congrats again, guys - it was a blast to launch with you! For what it’s worth, the ArduSat payload looks like it worked flawlessly… more details will be coming from them soon, but you can check out the results of one of their (SFE-provided) cameras here: http://twitpic.com/b80kzy.

Also, if you’re interested in the writeup of the EDGE flight specifically, check out the EDGE3 Mission Summary.

I checked current draw at both 3.7V and 4.0V, as well as with and without the LED, and didn’t notice a significant difference with or without the LED in place. A full writeup of the work that my team and I did with this camera (as well as information about the flight) can be found here (link to the HackHD review towards the bottom of the page): EDGE2 Flight Summary. I’ve only just started the public documentation process for this flight, so the payload info will be fleshed out over the next couple of weeks.

Interesting that you got a C4 card to work… I’ll have to try again with mine.

My team and I just flew this camera on a high-altitude balloon (HAB) here in Colorado over labor day weekend, and we were very impressed. The dynamic range on the camera is fantastic - a HAB flight has everything from looking straight at the sun to looking into “black space,” and this camera handled the transitions reasonably quickly and the scenes where the extremes were combined were well balanced with fine detail still very clear. We’ll get a link to the video up as soon as we’re done editing.

Over the space of 2.5 hours, we consumed 1660 mAH out of the single-cell lipo we were using, for an average of around 650mA current requirement during recording. When I hooked it up to my benchtop power supply, it looks like the current draw is a little bit bursty, bouncing between 600 and 700 mA rapidly during recording (perhaps buffering up data and then dumping it to the card).

Definitely get a good high-speed SD card for this camera - Class 4 doesn’t cut it (I didn’t expect it to, but wanted to try it anyway). Using a slow card results in stuttering video; we flew a Class 10 16g uSD, and saw about 13.4GB consumed over the 2.45 hour recording time.

All right - numbers are good! For a 10dBm (10mW) Tx with a 9dBi Tx antenna and just a touch of cable loss for good measure, I’m coming up with approx. 20dBi of Rx gain required for a comfortable fade margin at 50 miles out (just the baseline distance that I use), which is going to be a huge helical antenna with a pretty narrow beam. Difficult, but not impossible… here’s another online calculator, this one for helical antennas: http://www.daycounter.com/Calculators/Helical-Antenna-Design-Calculator.phtml
On your blog, you mention that the easyradio units are 433Mhz… all of the calculations that I’ve done so far are for 900MHz, which has substantially higher free space path loss. I just mention it becaus it’s a fairly substantial difference (50 miles = approx. 130dBm loss @ 900MHz, 123dBm loss @ 433)… let me know.
Also, FWIW, it may be possible to line up some additional equipment donations for you… I sent some contact info to the email address on your blog.
Good luck!

Ultimately, the goal should be to achieve a fade margin that’s higher than your noise floor for a given transmission distance. Fade margin is essentially what’s left over when you add up your transmit power, all of your gains (antennas, amplifiers, etc), losses (cables, connectors, free space path loss), and receiver sensitivity. Thanks to the beauty of using log-based units, link budget calculations really are just adding and subtracting!

I guess I’m going to assume that you’re using xTend modules, though you can feel free to correct me if that assumption is off base. Essentially, I just need to know what the Rx sensitivity is for your ground station, and the xTend’s -110dBm is a good place to start. If we assume that you’re transmitting 5mW (really low, BTW), which is about 7dBm, and put a 9dBi antenna on the payload, for a fade margin of 15 dBm at a distance of 50 miles (near the minimum that I’ve seen for solid performance, but I’m near to a fair bit of 900 MHz SCADA systems in my area) you’d need a ~20 dBi receive antenna, but this will provide challenges in that the beam width (essentially how wide the gain pattern is) will be narrow, meaning that you’d need to be fairly accurate with your antenna pointing out at the maximum distance. As mentioned earlier, circularly polarized antennas can help with spin-tolerance, which may be a good thing with low signal levels, but, without a SWR meter (at least – a vector network analyzer is better), it can be difficult to build and properly tune hand-made skew-planar and helical antennas.

I’m curious about why you’ve elected to run such a low transmit power… increasing it is very easy way to increase SNR, and the power requirements for broadcasting 1W out of an xTend are easily handled by a good 3-cell 2200mAH lipo.

Anyway, I hope that this helps… if I can be of further assistance, feel free to let me know. I’ll keep an eye here for a few more days. Good luck!

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